diff options
| author | Kevin O'Connor <kevin@koconnor.net> | 2018-03-29 14:15:16 -0400 |
|---|---|---|
| committer | Kevin O'Connor <kevin@koconnor.net> | 2018-03-29 16:40:26 -0400 |
| commit | b0b4bc8958d044cdd14ed23e5f7fe6d76bc1250b (patch) | |
| tree | 1470b09143624525160deea90159bf55c5daf475 | |
| parent | a6553538e6505447941979494d42d7477c045e31 (diff) | |
| download | kutter-b0b4bc8958d044cdd14ed23e5f7fe6d76bc1250b.tar.gz kutter-b0b4bc8958d044cdd14ed23e5f7fe6d76bc1250b.tar.xz kutter-b0b4bc8958d044cdd14ed23e5f7fe6d76bc1250b.zip | |
heater: Add some comments to the thermistor math
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
| -rw-r--r-- | klippy/heater.py | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/klippy/heater.py b/klippy/heater.py index d8021332..cac8f984 100644 --- a/klippy/heater.py +++ b/klippy/heater.py @@ -17,7 +17,8 @@ KELVIN_TO_CELCIUS = -273.15 class Thermistor: def __init__(self, config, params): self.pullup = config.getfloat('pullup_resistor', 4700., above=0.) - # Calculate Steinhart-Hart coefficents from temp measurements + # Calculate Steinhart-Hart coefficents from temp measurements. + # Arrange samples as 3 linear equations and solve for c1, c2, and c3. inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS) inv_t2 = 1. / (params['t2'] - KELVIN_TO_CELCIUS) inv_t3 = 1. / (params['t3'] - KELVIN_TO_CELCIUS) @@ -43,6 +44,7 @@ class Thermistor: def calc_adc(self, temp): inv_t = 1. / (temp - KELVIN_TO_CELCIUS) if self.c3: + # Solve for ln_r using Cardano's formula y = (self.c1 - inv_t) / (2. * self.c3) x = math.sqrt((self.c2 / (3. * self.c3))**3 + y**2) ln_r = math.pow(x - y, 1./3.) - math.pow(x + y, 1./3.) |